Carburetors are known for supplying fuel to an air flow passage of a carburetor or similar device where such fuel is mixed with air to form a combustible air/fuel mixture. Such carburetors have one or more fuel jets which are usually located in a venturi portion of the air flow passage, upstream of the throttle plate, such that the vacuum produced in the venturi portion helps draw fuel through the jet and into the air flow passage. Some carburetors may have multiple jets located in the air flow passage. For example, a slow jet may be provided for supplying fuel at idle or at low speeds and a main jet may be provided for supplying fuel at midrange or high speeds.
The main fuel jets used in such carburetors often have a flow controlling needle that is reciprocally contained within the fuel flow passage of the fuel jet. The amount of fuel delivered by the fuel jet is controlled by sliding the needle into or out of the fuel jet using a reciprocal slide that is mounted in the carburetor body. The upper end of the needle is connected to the slide such that vertical up and down movement of the slide is translated into vertical up and down movement of the needle. The needle includes a tapered section which creates a bigger gap between the outer diameter of the needle and the fuel flow passage of the fuel jet as the needle rises, thus increasing the fuel flow through the main jet as the needle rises in the main jet.
A vent hole is typically provided in the slide on the bottom of the slide. The Applicant has discovered that varying the size of the vent hole affects how quickly the slide moves up and down and, thus, affects the engine performance. However, in known slide carburetors, there is no way to easily and quickly adjust the size of the vent hole.